Electron paramagnetic resonance, optical and magnetic studies of Tb3+in lanthanide nicotinate dihydrates

Abstract

Optical absorption and fluorescence, magnetic susceptibility and electron magnetic resonance experiments have been made of Tb3+, 4f8, ions in lanthanide nicotinate dihydrate single crystals. Optical absorption spectroscopy in undiluted terbium nicotinate dihydrate (TbND) indicates that the ground state of Tb3+,7F6, is a singlet exhibiting a quadratic Zeeman effect, and this is confirmed by the observation of a temperature-independent Van Vleck paramagnetism below 4.2 K. This is what one would expect for a non-Kramers ion in a crystal field of no symmetry. In spite of this, electron paramagnetic resonance (epr) is observed from Tb3+ions both in dilute LaND containing 0.01 mole fraction of Tb and in TbND. In the dilute material, in spite of the absence of site symmetry, the results show a nearly degenerate non-Kramers doublet with agvalue of 17.2(8), close to the maximum possible value of 12gj; the ground state must therefore be predominantlyMj= ±6. The epr in TbND arises from some type of defect site involving two interacting dissimilar Tb3+ions. The spectrum of Tb3+ions observed by optical fluorescence is also attributed to defect sites.